/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkPositionIndexes;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.lang.reflect.Array;
import java.util.Arrays;
import java.util.Collection;
import javax.annotation.Nullable;

/**
 * Static utility methods pertaining to object arrays.
 *
 * @author Kevin Bourrillion
 * @since 2.0
 */
@GwtCompatible(emulated = true)
public final class ObjectArrays {

    private ObjectArrays() {}

    /**
     * Returns a new array of the given length with the specified component type.
     *
     * @param type the component type
     * @param length the length of the new array
     */
    @GwtIncompatible // Array.newInstance(Class, int)
    @SuppressWarnings("unchecked")
    public static <T> T[] newArray(Class<T> type, int length) {
        return (T[]) Array.newInstance(type, length);
    }

    /**
     * Returns a new array of the given length with the same type as a reference array.
     *
     * @param reference any array of the desired type
     * @param length the length of the new array
     */
    public static <T> T[] newArray(T[] reference, int length) {
        return Platform.newArray(reference, length);
    }

    /**
     * Returns a new array that contains the concatenated contents of two arrays.
     *
     * @param first the first array of elements to concatenate
     * @param second the second array of elements to concatenate
     * @param type the component type of the returned array
     */
    @GwtIncompatible // Array.newInstance(Class, int)
    public static <T> T[] concat(T[] first, T[] second, Class<T> type) {
        T[] result = newArray(type, first.length + second.length);
        System.arraycopy(first, 0, result, 0, first.length);
        System.arraycopy(second, 0, result, first.length, second.length);
        return result;
    }

    /**
     * Returns a new array that prepends {@code element} to {@code array}.
     *
     * @param element the element to prepend to the front of {@code array}
     * @param array the array of elements to append
     * @return an array whose size is one larger than {@code array}, with {@code element} occupying
     *         the first position, and the elements of {@code array} occupying the remaining
     *         elements.
     */
    public static <T> T[] concat(@Nullable T element, T[] array) {
        T[] result = newArray(array, array.length + 1);
        result[0] = element;
        System.arraycopy(array, 0, result, 1, array.length);
        return result;
    }

    /**
     * Returns a new array that appends {@code element} to {@code array}.
     *
     * @param array the array of elements to prepend
     * @param element the element to append to the end
     * @return an array whose size is one larger than {@code array}, with the same contents as
     *         {@code array}, plus {@code element} occupying the last position.
     */
    public static <T> T[] concat(T[] array, @Nullable T element) {
        T[] result = Arrays.copyOf(array, array.length + 1);
        result[array.length] = element;
        return result;
    }

    /**
     * Returns an array containing all of the elements in the specified collection; the runtime type
     * of the returned array is that of the specified array. If the collection fits in the specified
     * array, it is returned therein. Otherwise, a new array is allocated with the runtime type of
     * the specified array and the size of the specified collection.
     *
     * <p>
     * If the collection fits in the specified array with room to spare (i.e., the array has more
     * elements than the collection), the element in the array immediately following the end of the
     * collection is set to {@code null}. This is useful in determining the length of the collection
     * <i>only</i> if the caller knows that the collection does not contain any null elements.
     *
     * <p>
     * This method returns the elements in the order they are returned by the collection's iterator.
     *
     * <p>
     * TODO(kevinb): support concurrently modified collections?
     *
     * @param c the collection for which to return an array of elements
     * @param array the array in which to place the collection elements
     * @throws ArrayStoreException if the runtime type of the specified array is not a supertype of
     *         the runtime type of every element in the specified collection
     */
    static <T> T[] toArrayImpl(Collection<?> c, T[] array) {
        int size = c.size();
        if (array.length < size) {
            array = newArray(array, size);
        }
        fillArray(c, array);
        if (array.length > size) {
            array[size] = null;
        }
        return array;
    }

    /**
     * Implementation of {@link Collection#toArray(Object[])} for collections backed by an object
     * array. the runtime type of the returned array is that of the specified array. If the
     * collection fits in the specified array, it is returned therein. Otherwise, a new array is
     * allocated with the runtime type of the specified array and the size of the specified
     * collection.
     *
     * <p>
     * If the collection fits in the specified array with room to spare (i.e., the array has more
     * elements than the collection), the element in the array immediately following the end of the
     * collection is set to {@code null}. This is useful in determining the length of the collection
     * <i>only</i> if the caller knows that the collection does not contain any null elements.
     */
    static <T> T[] toArrayImpl(Object[] src, int offset, int len, T[] dst) {
        checkPositionIndexes(offset, offset + len, src.length);
        if (dst.length < len) {
            dst = newArray(dst, len);
        } else if (dst.length > len) {
            dst[len] = null;
        }
        System.arraycopy(src, offset, dst, 0, len);
        return dst;
    }

    /**
     * Returns an array containing all of the elements in the specified collection. This method
     * returns the elements in the order they are returned by the collection's iterator. The
     * returned array is "safe" in that no references to it are maintained by the collection. The
     * caller is thus free to modify the returned array.
     *
     * <p>
     * This method assumes that the collection size doesn't change while the method is running.
     *
     * <p>
     * TODO(kevinb): support concurrently modified collections?
     *
     * @param c the collection for which to return an array of elements
     */
    static Object[] toArrayImpl(Collection<?> c) {
        return fillArray(c, new Object[c.size()]);
    }

    /**
     * Returns a copy of the specified subrange of the specified array that is literally an
     * Object[], and not e.g. a {@code String[]}.
     */
    static Object[] copyAsObjectArray(Object[] elements, int offset, int length) {
        checkPositionIndexes(offset, offset + length, elements.length);
        if (length == 0) {
            return new Object[0];
        }
        Object[] result = new Object[length];
        System.arraycopy(elements, offset, result, 0, length);
        return result;
    }

    @CanIgnoreReturnValue
    private static Object[] fillArray(Iterable<?> elements, Object[] array) {
        int i = 0;
        for (Object element : elements) {
            array[i++] = element;
        }
        return array;
    }

    /**
     * Swaps {@code array[i]} with {@code array[j]}.
     */
    static void swap(Object[] array, int i, int j) {
        Object temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }

    @CanIgnoreReturnValue
    static Object[] checkElementsNotNull(Object... array) {
        return checkElementsNotNull(array, array.length);
    }

    @CanIgnoreReturnValue
    static Object[] checkElementsNotNull(Object[] array, int length) {
        for (int i = 0; i < length; i++) {
            checkElementNotNull(array[i], i);
        }
        return array;
    }

    // We do this instead of Preconditions.checkNotNull to save boxing and array
    // creation cost.
    @CanIgnoreReturnValue
    static Object checkElementNotNull(Object element, int index) {
        if (element == null) {
            throw new NullPointerException("at index " + index);
        }
        return element;
    }
}
